It is known to determine the steering center of a moving vehicle. This value is important to know for several different advanced vehicle functions, for example vehicle active yaw control.
Further, it is important to learn this value as early in the driving cycle as possible. The value that is saved in the vehicle""s memory when the vehicle is turned off will not be accurate if the steering wheel was turned while the vehicle was off.
One way of determining the steering center of a moving vehicle is the use of an absolute steering wheel angle sensor. An absolute steering wheel angle sensor provides the actual position of the steering wheel at any point in the vehicle""s driving cycle. These sensors are rather expensive averaging approximately $30 each.
On the other hand, relative steering wheel angle sensors sense movements of the steering wheel only. This type of sensor does not provide the absolute position of the steering wheel. Rather, in vehicle""s utilizing this type of sensor, the steering center position needs to be determined in each ignition cycle. In the beginning of the ignition cycle, it is not known whether the saved steering wheel angle is accurate since there is no way to determine if the steering wheel was turned while the vehicle was off. Relative steering wheel angle sensors average approximately $5 each. Therefore, it is desirable to use the relative steering wheel angle sensor to reduce the overall cost of the vehicle.
It is desirable to use the information that the relative steering wheel angle sensor yields to calculate an accurate absolute steering center value. To yield an accurate absolute steering center value, calculations need to be performed utilizing input from the relative steering wheel angle sensor and other vehicle sensors.
One known procedure for calculating a steering center is to use input from vehicle sensors while the vehicle is driving at a single predetermined speed to determine a steering center angle. This calculated steering center angle is compared with a table including accurate steering wheel angle values for different sensor inputs. The table is stored in the vehicle""s memory. If the calculated steering wheel angle value is within a predetermined range of the corresponding value stored in the table then the calculated steering wheel angle value is assumed to be the correct steering wheel angle value.
A first disadvantage of this known procedure is that a significant amount of memory is required to store the table. A second disadvantage is that, while the table requires a significant amount of memory it only involves data corresponding to one vehicle speed. A third disadvantage is that the most recent calculated steering wheel angle center value is assumed to be correct. A fourth disadvantage is that the procedure doesn""t take into account misalignments of the front axle.
Therefore, it is desirable to determine an accurate steering center value that is determined very early in the vehicle""s driving cycle, performing the minimal number of calculations as possible and utilizing the minimal amount of memory. Further, it is desirable to determine the steering wheel angle center at any vehicle speed and that is robust against misalignments of the front axle.
The present invention overcomes the disadvantages outlined above by providing a method for determining a vehicle""s steering wheel angle center utilizing a relative steering wheel angle sensor. Additionally, the present invention provides that information saved in the vehicle""s active yaw controller volatile memory will be saved for some period of time after the vehicle is shut down or so long as the vehicle is moving. This is advantageous for vehicles that have stalling problems.
The purpose of the present invention is to quickly determine and verify the accuracy of the steering center angle based on the direction of the vehicle""s motion from the vehicle""s yaw velocity, lateral acceleration, vehicle velocity, and other input signals. An advantage of the present invention is that the method can be performed while the vehicle is driving at any speed. In other words, it is not limited to accurate values for only one vehicle speed. Further, less memory is required since there is no look-up table that needs to be stored.
In fact, it is the steering center and not the steering wheel center that is found eventually. The invention determines when the yaw velocity is zero or when the vehicle is driving straight ahead, regardless of the position of the steering wheel at this time. Therefore, the invention is robust against misalignments of the front axle.
Further, the vehicle continuously monitors and updates the steering wheel angle.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.